From mboxrd@z Thu Jan 1 00:00:00 1970 From: john stultz Subject: Re: Clock jumps Date: Thu, 27 May 2010 17:46:45 -0700 Message-ID: <1275007605.1813.18.camel@work-vm> References: <20100525062100.GP22163@redhat.com> <4BFD5616.6070302@cora.nwra.com> <4D7E210A-4694-4B6E-B721-6024CE96ABC0@suse.de> <4BFEE8A2.30706@birkenwald.de> <1275004816.1813.15.camel@work-vm> <4BFF0F3F.9050800@birkenwald.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Thomas Gleixner , Ingo Molnar To: Bernhard Schmidt Return-path: Received: from e3.ny.us.ibm.com ([32.97.182.143]:49577 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755087Ab0E1Aqu (ORCPT ); Thu, 27 May 2010 20:46:50 -0400 In-Reply-To: <4BFF0F3F.9050800@birkenwald.de> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, 2010-05-28 at 02:33 +0200, Bernhard Schmidt wrote: > On 28.05.2010 02:00, john stultz wrote: > > Looking at the diff: > > --- dmesg-lenny 2010-05-27 16:45:33.000000000 -0700 > > +++ dmesg-squeeze 2010-05-27 16:46:14.000000000 -0700 > > @@ -132,8 +132,8 @@ > > console [ttyS1] enabled > > hpet clockevent registered > > Fast TSC calibration using PIT > > -Detected 2660.398 MHz processor. > > -Calibrating delay loop (skipped), value calculated using timer frequency.. 5320.79 BogoMIPS (lpj=10641592) > > +Detected 2613.324 MHz processor. > > +Calibrating delay loop (skipped), value calculated using timer frequency.. 5226.64 BogoMIPS (lpj=10453296) > > Security Framework initialized > > Dentry cache hash table entries: 524288 (order: 10, 4194304 bytes) > > Inode-cache hash table entries: 262144 (order: 9, 2097152 bytes) > > @@ -160,7 +160,7 @@ > > CPU0: Intel(R) Xeon(R) CPU 3075 @ 2.66GHz stepping 0b > > Booting Node 0, Processors #1 > > Brought up 2 CPUs > > -Total of 2 processors activated (10640.79 BogoMIPS). > > +Total of 2 processors activated (10546.63 BogoMIPS). > > NET: Registered protocol family 16 > > ACPI: bus type pci registered > > PCI: MMCONFIG for domain 0000 [bus 00-ff] at [mem 0xe0000000-0xefffffff] (base 0xe0000000) > > > > So you can see in the above the during the second boot the TSC > > calibration was badly mis-calculated. This was the cause of the skew. > > > > Not sure how that might be linked to the distro upgrade. It could have > > been something like SMI damage during the calibration time, but I > > thought the calibration loop watched for that. > > > > Bernhard: I expect with all those vms, this machine isn't rebooted > > frequently. So could you look at the logs to see how much the "Detected > > xxxx.yyy MHz processor." line varies by across a few other boots (if > > they still exist?). > > Correct, the box isn't rebooted often, but I do have a few dmesg outputs > laying around. lpj was always almost the same until the very last boot > which screwed up the clock. > > dmesg:[ 0.000000] Linux version 2.6.33 (root@svr02) (gcc version > 4.3.2 (Debian 4.3.2-1.1) ) #1 SMP Sun Mar 7 23:01:45 CET 2010 > dmesg:[ 0.008005] Calibrating delay loop (skipped), value calculated > using timer frequency.. 5226.64 BogoMIPS (lpj=10453296) > dmesg:[ 0.288002] Total of 2 processors activated (10546.63 BogoMIPS). Yea. The bogomips/loops per jiffies are actually calculated with a different chunk of code (although its interesting it miscalculated in both cases). Could you send the "Detected xxxx.yyy MHz processor." lines as well? thanks -john